Proton conducting electrode, method for preparation thereof and electro-chemical device

ABSTRACT

A proton conducting electrode is provided. The proton conducting electrode includes a mixture of a fullerene derivative and an electron conducting catalyst, wherein the fullerene derivative is composed of carbon atoms that can form fullerene molecules and one or more proton (H + ) dissociating groups introduced into said carbon atoms. The proton conducting electrode can be manufactured by coating a mixture containing the fullerene derivative and the electron conducting catalyst on a gas transmitting current collector. The proton conducting electrode can be used in a variety of applications, such as in electrochemical devices, including fuel cells.

RELATED APPLICATION DATA

The present application claims priority to Japanese Patent Document No.P2000-239839 herein incorporated by reference to the extent permitted bylaw.

BACKGROUND OF THE INVENTION

The present invention relates to a proton (H⁺) conducting electrode, amethod for its preparation and to an electro-chemical device employing aproton conducting electrode.

A variety of electro-chemical devices, constructed on the basis of areaction of decomposition of a hydrogen gas, or a chemical substancecontaining hydrogen atoms, on an electrode to yield protons (H⁺) andelectrons, a reaction of protons and electrons to yield hydrogen, or areaction of protons, electrons and oxygen or another substance to yieldwater or a further substance, such as fuel batteries or otherproton-type batteries, or chemical sensors, have been proposed.

Since electrons, protons and other substances, such as hydrogen gas,oxygen gas or water, are involved in the above various reactions, thesite where all of these substances meet together represents a sole siteof reaction.

For example, if a catalyst exhibiting electronic conductivity issupplied in a more or less dispersed state onto the surface of a protonconductor, the contact point between the protonic conductor andelectrons and in its vicinity represent a site where protons, electronsand other gaseous substances can exist together. In general, such siteis termed a three-phase interface.

FIG. 1 shows a prior-art example of an electrode structure. In theelectrode structure, shown in FIG. 1, a catalyst 3 exhibiting electronicconductivity is dispersed on the surface of a proton conductor 1, withthe surface of the catalyst being then covered by a gas transmittingcurrent collector 5. If only the surface of the proton conductor 1, withthe catalyst 3 dispersed thereon, is used for the reaction yielding theprotons (H⁺) and electrons, a three-phase interface 7 is present in thevicinity of contact points of the proton conductor 1 and the catalyst 3.However, the site where all of electrons (e⁻) 4, protons (H⁺) 8 andgases 6, such as hydrogen gas or oxygen gas, meet together, is limitedto a point-like area, this point-like area serving as a sole three-phaseinterface, with the result that the function as the electrode is notmanifested satisfactorily.

Currently, for improving the function as an electrode, such a techniqueis used which consists in mixing proton-conducting components into anelectrode material for forming a three-phase interface on the surface ofthe protonic conductor throughout the entire electrode formed to acertain thickness.

With this technique, electronic conducting paths are formed in a meshedpattern within the electrode by the catalyst itself or by anelectrically conductive assistant material specifically mixed into theelectrode material, whilst the proton conductor contained is also formedin a meshed pattern. If the other component than protons and electronsis a gas, the electrode itself is to be porous to allow the gas to bepermeated throughout the electrode. If the other component is not a gasbut a solid phase, the solid phase is added to the electrode. In any ofthese cases, the three-phase interface is to be formed over the entireelectrode, as described above, to provide for as many reaction points aspossible to improve the function as the electrode.

It is noted that, in the above electrode operating at a temperaturelower than 100° C., inclusive of the ambient temperature, a protondissociating liquid or a proton conducting high-polymer solidelectrolyte, such as Nafion, manufactured by Du Pont, de Nemur, iscurrently used as the protonic conductor mixed into the electrode. Inparticular, with the use of Nafion, the device may be solidified, andhence may find extensive application. Thus, the device tends to be usedextensively as a fuel battery for low temperature.

However, Nafion, which is a solid material, suffers a problem that, byreason of its proton conduction mechanism, its proton conductionperformance is not displayed except if the Nafion itself is soaked witha sufficient amount of water. Thus, if Nafion is contained in anelectrode, the device is difficult to use continuously under a dryatmosphere.

A need therefore exists to provide an improved proton conductingelectrode that can be readily made and effectively used.

SUMMARY OF THE INVENTION

In view of the above-described status of the art, it is an advantage ofthe present invention to provide a proton conducting electrode in whichthree-phase interface exists abundantly within the electrode and whichnot only has enhanced properties as electrode but exhibits only smallatmosphere dependency, a method for its preparation, and anelectro-chemical device.

In an embodiment, the present invention provides a proton conductingelectrode including a mixture that includes a fullerene derivative andan electron conducting catalyst, wherein the fullerene derivative iscomposed of carbon atoms forming fullerene molecules and a protondissociating group introduced into the carbon atoms.

As used herein, the term “proton dissociating group” or the like means afunctional group capable of releasing protons on electrolyticdissociation, and the term “dissociation of protons (H⁺)” or the likemeans separation of protons from the functional group on electrolyticdissociation.

Since the proton conducting electrode of the present invention iscomprised of the fullerene derivative having the capability of protondissociation, and the electron conducting catalyst, a three-phaseinterface can be made to exist in a sufficient quantity in the electrodeand hence has enhanced properties with respect to, for example,generating and propagating the protons.

Since the proton conducting electrode of the present invention uses thefullerene derivative, it exhibits only negligible atmosphere dependencyallowing it to have enhanced proton conductivity even in a dryatmosphere. However, it may also be used in the presence of themoisture.

The proton conducting electrode according to an embodiment of thepresent invention is prepared by a method that includes coating amixture of a fullerene derivative, composed of carbon atoms formingfullerene molecules and a proton dissociating group introduced into thecarbon atoms, on a gas transmitting current collector.

Since the proton conducting electrode according to an embodiment of thepresent invention can be produced by a step of coating theabove-mentioned mixture on the gas transmitting current collector, theparticle distribution density can be adjusted with relative ease.Moreover, since the mixture can be coated in multiple layers, a desiredfilm thickness can be produced.

The electrochemical device according to an embodiment of the presentinvention includes a first electrode, a second electrode and a protonconductor sandwiched or disposed between these first and secondelectrodes, wherein a proton conducting electrode comprising of amixture of a fullerene derivative and an electron conducting catalyst,wherein the fullerene derivative is composed of carbon atoms formingfullerene molecules and a proton dissociating group introduced into thecarbon atoms, forms at least the first electrode of the first and secondelectrodes.

In the electro-chemical device according to an embodiment of the presentinvention, in which at least the first electrode of the first and secondelectrodes is constructed by the proton conducting electrode, composedof the fullerene derivative and the catalyst, enhanced current densityand output characteristics can be achieved. The electrochemical devicecan function without moisture, allowing it to have enhanced propertieseven under a dry atmosphere, and can be used continuously.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the Figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic cross-sectional view showing a conventionalelectrode employing a proton conductor.

FIGS. 2A and 2B show molecular structures of C₆₀ and C₇₀, respectively.

FIGS. 3A and 3B show structures of fullerene polyhydroxide as afullerene derivative according to an embodiment of the presentinvention.

FIGS. 4A and 4B are schematic views showing examples of fullerenederivatives according to an embodiment of the present invention.

FIGS. 5 and 6 are schematic views showing examples of a proton conductoraccording to an embodiment of the present invention.

FIG. 7 is a schematic view showing an example of a proton conductoraccording to an embodiment of the present invention.

FIG. 8 schematically shows a structure of a fuel battery employing aproton conducting electrode according to an embodiment of the presentinvention.

FIG. 9A shows an electrical equivalent circuit of a pellet made pursuantto an embodiment of the present invention.

FIG. 9B shows an equivalent electrical circuit of a pellet made withfullerene molecules without proton dissociating properties.

FIG. 10 is a graph showing complex impedance measurements with respectto an experimental study as described below.

FIG. 11 is a graph showing the temperature dependency of the protonicconductivity of a pellet made pursuant to an embodiment of the presentinvention.

FIG. 12 shows the comparative results of power generation of a fuelbattery employing a proton conducting electrode according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally relates to proton conducting materials.More specifically, the present invention relates to electrodes,electro-chemical devices, other suitable devices and methods ofpreparing and using same that employ proton conducting materials, suchas fullerene-based materials that have proton dissociating properties.

It should be appreciated that there is no particular limitation tofullerene molecules, as a matrix into which proton dissociating groups,used in accordance with an embodiment of the present invention, are tobe introduced, provided that they are spherically-shaped clustermolecules. However, fullerene molecules per se, as selected from C₁₄,C₂₀ (see FIG. 2A), C₇₀ (see FIG. 2B), C₇₆, C₇₈, C₈₀, C₈₂ or C₈₄, ormixtures of two or more of these fullerene molecules, are usuallypreferred.

These fullerene molecules were discovered in the mass spectrograph of acluster beam by laser ablation of carbon in 1985 (Kroto, H. W.; Heath,J. R.; O'Brien, S. C.; Curl, R. F.; Smalley, R. E. Nature 1985.318,162).The manufacturing method was actually established five years later. Thatis, in 1990, the manufacturing method by the arc discharge method ofcarbon electrodes was found and, since that time, fullerene attractednotice as being a carbonaceous semiconductor material.

The present inventors have conducted a variety of research into theproton conductivity of derivatives of fullerene molecules, and foundthat fullerene polyhydroxide, obtained on introducing hydroxy groupsinto the constituent carbon atoms of fullerene, exhibits high protonicconductivity over a wide temperature range inclusive of an ambienttemperature range, that is over a temperature range of at least 160° C.to about 40° C., inclusive of the solidifying point and boiling point ofwater. It was also found that this protonic conductivity becomes moreenhanced when a hydrogen sulfate ester group is introduced in place ofthe hydroxy group into the constituent carbon atoms of fullerene.

More specifically, fullerene polyhydroxide is a generic term ofcompounds that include fullerene and a number of hydroxy groups addedthereto, as shown in FIGS. 3A and 3B, and is commonly referred to asfullerenol. As a matter of course, the number of hydroxy groups or thearrangement thereof in the molecular structure may be varied in a numberof suitable ways. Synthesis examples of fullerenol were first reportedin 1992 by Chiang et al (Chiang, L. Y.; Swirczewski, J. W.; Hsu, C. S.;Chowdhury, S. K.; Cameron, S.; Creegan, K., J. Chem. Soc., Chem. Commu.1992, 1791). Since that time, fullerenol, having hydroxy groupsintroduced in more than a preset amount therein, has attracted notice inparticular as to its water-solubility, and has been researched mainly inthe bio-related technical field.

The present inventors have formed fullerenol into an aggregate, as shownschematically in FIG. 4A, so that interaction will be produced betweenhydroxy groups of proximate fullerenol molecules, indicated by thecircle symbols in the drawing, and have uniquely found, that thisaggregate exhibits high protonic conductivity, in other words,dissociation of H⁺ from phenolic hydroxy groups of the fullerenolmolecules, as a macroscopic mass.

In an embodiment, the present invention can include a fullereneaggregate, having a number of —OSO₃H groups, in addition to fullerenol,as a proton conductor. Fullerene polyhydroxide, in which OSO₃H groupstake the place of one or more OH groups, as shown in FIG. 4B, that ishydrogen sulfate ester type fullerenol, was also reported by Chiang etal in 1994 (Chiang. L. Y.; Wang, L. Y.; Swirczewski, J. W.; Soled, S.;Cameron, S., J. Org. Chem. 1994, 59, 3960). It should be noted that onlyOSO₃H groups or a number of each of this group and the hydroxy group mayalso be contained in one molecule of the hydrogen sulfate ester typefullerenol.

As for the protonic conductivity, demonstrated on aggregating a largequantity of the above-mentioned fullerene derivative into a bulkmaterial, the protons derived from the large number of hydroxy groupsand/or OSO₃H groups, inherently contained in the fullerene molecules,directly take part in migration, so that there is no necessity ofcapturing hydrogen or protons, derived from e.g., water vapor molecules,from atmosphere, or of replenishing water from outside, in particular,absorbing water from outside, there being no constraint imposed on theatmosphere to be in use. On the other hand, fullerene, forming the basisof these derivative molecules, can exhibit electrophilic properties,which are felt as significantly contributing to the promotion ofionization of hydrogen ions not only in highly acidic OSO₃H groups butalso in hydroxy groups. This accounts for excellent protonicconductivity of the proton conductor of the present invention.

Moreover, since a larger amount of hydroxyl and/or OSO₃H groups can beintroduced into one fullerene molecule, the number density of protonstaking part in conduction per unit volume of the conductor is increasedappreciably. This also accounts for an effective conductivity displayedby the proton conductor of the present invention.

A substantial portion of the proton conductor of the present inventionis constituted by carbon atoms of fullerene, so that it is light inweight, unsusceptible to deterioration and is free of pollutants. Themanufacturing cost of fullerene is also being lowered precipitously.Thus, in the light of resources, environment and economical merits,fullerene is believed to be a desirable carbonaceous material ascompared to other comparable materials.

It should be appreciated that Applicants' investigations have revealedthat the proton dissociating group does not have to be limited tohydroxyl groups and/or OSO₃H groups.

Thus, it is sufficient if this dissociating group is represented by —XH,with X being an atom or group of atoms having divalent bonds. It is alsosufficient if this group is represented by —OH or —YOH, with Y being anarbitrary atom or group of atoms having divalent bonds.

In an embodiment, the proton dissociating group may be any one of —COOH,—SO₃H or —PO(OH)₂, in addition to —OH and —OSO₃H, like groups andcombinations thereof.

For synthesizing a fullerene derivative, used in a proton conductingelectrode according to an embodiment of the present invention, it issufficient if any suitable proton dissociating group is introduced intoconstituent carbon atoms of fullerene molecules, by applying knownprocessing techniques, such as acid processing or hydrolysis, in anysuitable combination, to the powders of fullerene molecules.

According to an embodiment of the present invention, the mixturecontaining fullerene derivatives and electron conducting catalysts aredesirably porous, with the porosity being preferably in a range of about1% to about 90%. This enables the gas to be diffused to the entireelectrode so as to form a three-phase interface in the entire electrodeto increase the number of reaction points to improve the function of theelectrode in generating and propagating protons.

The mixing ration by weight of the fullerene derivatives and thecatalyst in the mixture containing fullerene derivatives and theelectron conducting catalyst is preferably 1:100 to 100:1.

Moreover, the mixture is preferably formed in a layered form on a gastransmitting current collector, such as carbon paper. The mixture may bepresent as a sole layer or in a multi-layer structure.

The proton conducting electrode according to an embodiment of thepresent invention includes a gas transmitting current collector on whicha mixture composed of the fullerene derivatives and the electronconducting catalyst is formed as a sole layer or in a multi-layerstructure, as described above, as shown in FIGS. 5 and 6.

In the proton conducting electrode, shown in FIG. 5, a porous mixture,containing the fullerenol molecules 2 as a fullerenol derivative and theelectron conducting catalyst 3, is diffusively coated on the surface ofthe proton conductor 1, with the surface of the porous mixture thenbeing coated with the gas transmitting current collector 5.

On the other hand, the proton conducting electrode, shown in FIG. 6, isobtained on coating a porous mixture of fullerenol molecules 2 and anelectron conducting catalyst 3 in multiple layers.

The proton conducting electrode of an embodiment of the presentinvention, constructed as shown in FIGS. 5 and 6, uses a porous mixturecontaining fullerenol molecules 2 and the electron conducting catalyst3, so that the gas can be permeated throughout the entire electrode.Moreover, since the fullerenol molecules 2 as a fullerene derivativehaving a proton dissociating capability and the electron conductingcatalyst 3 are formed throughout the inside of the electrode, there isproduced a three-phase interface 7 not only in the vicinity of a contactpoint between the proton conductor 1 and the catalyst 3, but also in thevicinity of a contact point between the catalyst 3 and the fullerenolmolecules 2. This three-phase interface 7 is a site where the electrons(e⁻) 4, protons (H⁺) and the gases 6, such as hydrogen or oxygen gasesall meet simultaneously.

Since the proton conducting electrode of the present invention iscapable of producing the three-phase interface 7 not only in thevicinity of the contact point between the proton conductor 1 and thecatalyst 3, but also in the vicinity of the contact point between thecatalyst 3 and the fullerenol molecules 2, the function of the electrodein generating and propagating protons can be improved. Additionally,since the proton conducting electrode contains the fullerene derivativehaving the proton dissociating capability, the electrode can be usedcontinuously even in a dry atmosphere.

The catalyst forming a porous mixture used in the proton conductingelectrode according to an embodiment of the present invention ispreferably formed of the porous material carrying electron conductingatoms. In this case, the amount of electron conducting atoms, carried bythe porous material, is preferably about 10 wt % to about 50 wt %.

The atoms exhibiting electron conductivity (catalytic metal) may beplatinum, ruthenium, vanadium, tungsten, the like or mixtures thereof,where the porous material may be carbon powders, porous Ni—Cr sinteredmaterial, Al₂O₃ sintered material, a porous plate of Li—Cr alloy, likematerials or combinations thereof. Of these, the combination of platinumand carbon powders is desirable.

Preferably, electron conducting atoms are present in an amount of about0.1 mg/cm² to about 10 mg/cm² between the proton conductor 1 and the gastransmitting current collector 5.

The proton conducting electrode according to an embodiment of thepresent invention can be used with advantage in a variety ofelectrochemical devices. That is, in a basic structure including firstand second electrodes and a proton conductor sandwiched or disposedbetween these electrodes, at least the first one of the first and secondelectrodes may be the proton conducting electrode embodying the presentinvention.

The proton conducting electrode embodying the present invention may beused, for example, in an electrochemical device in which at least one ofthe first and second electrodes is a gas electrode.

The fuel battery employing the proton conducting electrode of thepresent invention is hereinafter explained.

The mechanism of proton conduction of a fuel cell according to anembodiment of the present invention is as shown in the schematic view ofFIG. 7. A proton conduction unit 9 is sandwiched between a firstelectrode 10, for example, a hydrogen electrode, and a second electrode11, for example, an oxygen electrode, and dissociated protons (H⁺) aremigrated from the first electrode 10 towards the second electrode 11, asindicated by arrow in the drawing.

FIG. 8 shows an exemplary fuel cell employing the proton conductingelectrode according to an embodiment of the present invention. As shownin FIG. 8, this fuel cell includes a negative electrode 10, having aterminal 15 at one end, and which uses the proton conducting electrodeaccording to the present invention, and a positive electrode 11, havinga terminal 16 at one end, and which also uses the proton conductingelectrode. In an embodiment, the negative electrode 10 can include ahydrogen fuel electrode, whereas the positive electrode 11 can includean oxygen electrode. It should be appreciated that it is not required touse the proton conducting electrode of the present invention as thepositive electrode 11. The negative electrode 10 and the positiveelectrode 11 are arranged parallel to and facing each other, and theproton conduction unit 9 is sandwiched between the negative electrode 10and the positive electrode 11, as shown in FIG. 8.

In use of the fuel battery, constructed as shown in FIG. 8, hydrogenacting as a fuel 19 is sent via an inlet 17 at the negative electrode 10so as to be discharged at an optional exit port 18. A fuel (H₂) 19,supplied through inlet 17, yields protons as it traverses a flow channel20, these protons migrating along with the protons generated in thenegative electrode 10 and protons generated in the proton conductionunit 9 towards the positive electrode 11 where the protons are reactedwith oxygen (air) 24 supplied from the inlet 21 to the flow channel 22and which is then sent towards an exhaust port 23, thereby producing thedesired electromotive force.

With the fuel battery of the present invention, employing the protonconducting electrode of the present invention, and constructed as shownin FIG. 8, protons are dissociated in the negative electrode 10 and, asthe protons are dissociated in the proton conduction unit 9, the protonssupplied from the negative electrode 10 are migrated towards thepositive electrode 11, thus improving proton conductivity. Consequently,with the fuel battery of the present invention, no humidifying deviceetc is needed, so that the system is simplified and reduced in weight,while the function of the electrode, such as electrical density oroutput characteristics, may be improved.

In the electrochemical device, such as fuel battery or fuel cell,embodying the present invention, there is no particular limitation tothe proton conductor sandwiched between the proton conductingelectrodes, such that any suitable material exhibiting protonconductivity, such as fullerene hydroxide, hydrogen sulfate ester typefullerenol or Nafion, for example, may be used.

By way of example and not limitation, the following examples areprovided to illustrate various embodiments of the present invention.

EXAMPLE

<Synthesis of Fullerene Polyhydroxide>

This synthesis was carried out using a reference material (Chiang, L.Y.; Wang. L. Y.; Swirczewski. J. W.; Soled, S.; Cameron, S., J. Org.Chem. 1994, 59, 3960). 2 g of powders of C₆₀/C₇₀ fullerene mixture,containing approximately 15% of C₇₀, were charged into 30 ml of fumingsulfuric acid and stirred for three days in a nitrogen atmosphere as thetemperature was maintained at 60° C. The resulting reaction mass wascharged gradually into anhydrous diethyl ether cooled in a glacial bath.The resulting precipitates were fractionated on centrifugation, washedthree times with diethyl ether and twice with a 2:1 liquid mixture ofdiethyl ether and acetonitrile and dried under reduced pressure at 40°C. The dried product was charged into 60 ml of ion exchanged water andstirred for ten hours under bubbling with nitrogen at 85° C. Thereaction product was freed on centrifugation from precipitates whichwere washed several times with pure water, repeatedly centrifuged anddried under reduced pressure at 40° C. The resulting brownish powderswere subjected to FT-IR measurement. It was found by this measurementthat the IR spectrum of the brownish powders approximately coincidedwith that of C₆₀(OH)₁₂, thus indicating that the powders were fullerenepolyhydroxide powders as a target material. The above reaction can berepresented for C₆₀ as follows:

<Preparation of Flocculated Pellets of Fullerene Polyhydroxide>

90 mg of powders of fullerene polyhydroxide were taken and pressed inone direction into circular pellets 15 mm in diameter. The pressingpressure at this time was approximately 5 ton/cm². It was found that thepowders of fullerene polyhydroxide, while containing no binder resin orthe like, were superior in moldability and could be formed into a pelletextremely readily. This pellet, about 300 μm in thickness, is termed aflocculated pellet of fullerene polyhydroxide.

<Synthesis of Fullerene Polyhydroxide Hydrogen Sulfate Ester (FullEster)>

This synthesis was carried out using the above-mentioned referencematerial. 1 g of powders of fullerene polyhydroxide, was charged into 60ml of fuming sulfuric acid and stirred for three days in a nitrogenatmosphere at ambient temperature. The resulting reaction mass wascharged gradually into anhydrous diethyl ether cooled in a glacial bath.The resulting precipitates were fractionated on centrifugation, washedthree times with diethyl ether and twice with a 2:1 liquid mixture ofdiethyl ether and acetonitrile and dried under reduced pressure at 40°C. The resulting brownish powders were subjected to FT-IR measurement.It was found by this measurement that the IR spectrum of the brownishpowders approximately coincided with that of a compound all hydroxygroups of which are turned into a hydrogen sulfate ester, as indicatedin the above reference material, thus indicating that the powders werefullerene polyhydroxide hydrogen sulfate ester as a target material.

The above reaction can be represented for C₆₀(OH)₃ as follows(hereinafter the same):

<Preparation of Flocculated Pellets of Fullerene Polyhydroxide HydrogenSulfate Ester>

70 mg of powders of fullerene polyhydroxide hydrogen sulfate ester weretaken and pressed in one direction into circular pellets 15 mm indiameter. The pressing pressure at this time was approximately 5ton/cm². It was found that the powders, containing no binder resin orthe like, were superior in moldability and could be pelletized extremelyreadily. This pellet, about 300 μm in thickness, is termed a flocculatedpellet of fullerene polyhydroxide hydrogen sulfate ester.

<Preparation of Flocculated Fullerene Pellet of Comparative Example>

For comparison, 90 mg of fullerene, used as a starting material forsynthesis in the previous Example, were taken and pressed in onedirection into circular pellets 16 mm in diameter. The pressing pressureat this time was approximately 5 ton/cm². It was found that the powders,containing no binder resin or the like, were superior in moldability andcould be pelletized extremely readily. This pellet, about 300 μm inthickness, is termed a pellet of the Comparative Example.

Measurement of Proton Conductivity of Example (Flocculated Pellet ofFullerene Polyhydroxide Hydrogen Sulfate Ester) and Pellet ofComparative Example

For measuring the conductivity of the pellets of the Example and theComparative Example, each of the pellets was sandwiched between a pairof aluminum plates, each being 15 mm in diameter as is the pellet. An ACvoltage of an amplitude of 0.1 V was applied to each assembly, with afrequency ranging from 7 MHz to 0.01 Hz, to measure the compleximpedance at each frequency. The measurement was conducted in a dryatmosphere.

In measuring the impedance, the proton conduction unit 9 of the protonconductor of the above-described embodiment, comprised of the pellet,electrically forms an equivalent circuit, shown in FIG. 9A, and formscapacitances 14 a, 14 b across the first and second electrodes 10, 11and the proton conduction unit 9 represented by a parallel connection ofa resistance and a capacitance where a capacitance 13 represents thedelay effect on proton migration (phase delay for a high frequency),while a resistance 12 represents a parameter of proton mobility.

The complex impedance Z is represented by Z=Re(Z)+i·Im(Z). The frequencydependency of the proton conduction unit, represented by theabove-described equivalent circuit, was checked.

FIG. 9B shows an equivalent circuit in case of using the ordinaryfullerene molecules not having proton dissociating properties, as in theabove-described Comparative Example. In FIG. 9B, the equivalent circuitrepresents a capacitor 14 that includes an insulator 9 a (i.e., thefullerene pellet) disposed between a first electrode 10 and a secondelectrode 11.

FIG. 10 shows the results of impedance measurement for the pellets inthe Example and in the Comparative Example.

It may be seen from FIG. 10 that the frequency response of the compleximpedance of the Comparative Example as shown at B is approximatelysimilar to a response of a single capacitor as expressed by theequivalent circuit in FIG. 9B while the conduction behavior of chargedparticles, such as electrons or ions of the flocculated mass of thefullerene itself, was not measurable. Conversely, in the Example, anextremely fine semi-circular arc, though somewhat flat, may be observedin a high frequency portion as shown at A in FIG. 10. This indicatesthat there exists some conduction behavior of charged particles withinthe pellet of the Example. Additionally, there may be noticed an acuterise of the imaginary portion of the impedance in the low frequencyregion. This indicates that blocking of charged particles with thealuminum electrode occurs as the DC voltage is approached. Since thecharged particles on the side aluminum electrode are naturallyelectrons, it may be seen that the charged particles within the pelletof the Example are the particles other than electrons or holes, that isions. Judging from the structure of fullerenol used, this suggests thatthe charged particles are protons.

The conductivity of the charged particles can be found from the X-axisintercept of the arc seen towards the high frequency side. In the pelletof the Example, it may be calculated to be approximately 5×10⁻⁶ S/cm. Itcould be found that the flocculated mass of this type of fullerenederivative allows proton conduction at ambient temperature in a dryatmosphere.

Using the pellet of the Example (flocculated pellet of fullerenepolyhydroxide hydrogen sulfate ester), the above-mentioned measurementof the complex impedance was conducted in a temperature range from 160°C. to −40° C., to check for temperature dependency of the conductivityas found from the arc on the side high frequency. The results are shownas an Arrhenius plot in FIG. 11, from which it may be seen that theconductivity is changed linearly in a temperature range from 160° C. to−40° C. In short, this figure shows that the sole ion conductionmechanism can proceed in the above temperature range. That is, theflocculated mass of the fullerene derivative used in the presentinvention allows for proton conduction in a broad temperature rangeinclusive of the ambient temperature, in particular, even at an elevatedtemperature of 160° C. or a low temperature of −40° C.

Preparation of Fuel Batteries of Example and Comparative Example andPower Generation Test

Powders of carbon carrying 20 wt % of platinum (mean particle size: 50nm) and powders of fullerene polyhydroxide hydrogen sulfate ester,obtained as described above, were mixed together at a weight ratio of1:2 and mixed in a solution of tetrahydrofuran (THF). The resultingmixture was coated on a carbon paper to a platinum carrying amount of 1mg/cm² to form a fullerenol containing electrode of the presentinvention to a thickness of 50 μm.

Two fullerenol containing electrodes according to an embodiment of thepresent invention were prepared to form a fuel battery device thatincluded the electrodes placed on both sides of a thin film of aflocculated mass of the powders of fullerene polyhydroxide (thickness:25 μm) as a proton conductor. This fuel battery device was built in thefuel battery cell shown in FIG. 8. The one side (negative electrodeside) and the other side (positive electrode side) of the fuel batterydevice shown in FIG. 8 were opened to a dry hydrogen gas and to a dryoxygen gas, respectively, to carry out a power generation test atambient temperature.

By way of a Comparative Example, carbon powders (mean particle size: 50nm) carrying 20 wt % of platinum were coated on a carbon paper, using aNafion solution, to a platinum carrying amount of 1 mg/cm² and theNafion quantity of 2 mg/cm², to prepare a Nafion mixture electrode.

Two electrodes of the Nafion mixture were prepared and placed on eithersides of a thin film composed of powders of fullerene polyhydroxide(thickness: 25 μm) to prepare a fuel battery device, which then wasbuilt into a fuel battery cell shown in FIG. 8. The one side (negativeelectrode side) and the other side (positive electrode side) of the fuelbattery device shown in FIG. 8 were opened to a dry hydrogen gas and toa dry oxygen gas, respectively, to carry out a power generation test atambient temperature.

The results of each power generation test are shown in FIG. 12.

These results indicate that, while the open voltage is approximately 1.2V for both the Example and the Comparative Example, the Exampleemploying the electrode of the fullerenol mixture shows characteristicsshown at A in FIG. 12. That is, the Example is improved in currentdensity and has enhanced output characteristics as compared to theComparative Example of the electrode of the Nafion mixture shown at B inFIG. 12.

Since the proton conducting electrode, in an embodiment of the presentinvention, is a mixture of a fullerene derivative and an electronconducting catalyst, in which the fullerene derivative is composed ofcarbon atoms forming fullerene molecules and proton dissociating groupsintroduced therein, a three-phase interface can be present in asufficient quantity in the electrode, so that the electrode has enhancedproperties for generating and propagating protons.

Moreover, since the proton conducting electrode uses a fullerenederivative, it is low in atmosphere dependency and can be usedcontinuously even in a dry atmosphere, so that it is able to demonstrateenhanced proton conductivity which is desirable in the electro-chemicaldevice.

Since no atmosphere constraint is placed on the electro-chemical device,employing the proton conducting electrode according to an embodiment ofthe present invention, the system can be reduced in size and simplifiedin structure, while it is possible to develop optimum current densityand output characteristics.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the scope and spirit of the present invention andwithout diminishing its intended advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

1. A proton conducting electrode comprising a mixture including afullerene derivative and an electron conducting catalyst, wherein thefullerene derivative is composed of carbon atoms forming fullerenemolecules that have a proton dissociating group introduced into thecarbon atoms.
 2. The proton conducting electrode according to claim 1wherein the proton dissociating group is —XH, where X is an atom havinga divalent bond, and H is a hydrogen atom.
 3. The proton conductingelectrode according to claim 1 wherein the proton dissociating group isselected from the group consisting of OH and —YOH, where Y is selectedfrom the group consisting of an atom having a divalent bond and a groupof atoms having a divalent bond.
 4. The proton conducting electrodeaccording to claim 3 wherein the proton dissociating group is selectedfrom the group consisting of —OH, —OSO₃H, —COOH, —SO₃H, —PO(OH)₃ andmixtures thereof.
 5. The proton conducting electrode according to claim1 wherein the mixture is porous.
 6. The proton conducting electrodeaccording to claim 1 wherein the mixture has a structure selected fromthe group consisting of a single-layer structure and a multi-layerstructure.
 7. The proton conducting electrode according to claim 1wherein a mixing ratio by weight of the fullerene derivative and thecatalyst in the mixture ranges from about 1:100 to about 100:1.
 8. Theproton conducting electrode according to claim 1 wherein the mixture hasa porosity of about 1% to about 90%.
 9. The proton conducting electrodeaccording to claim 1 wherein the mixture is formed as a layer on a gastransmitting current collector.
 10. The proton conducting electrodeaccording to claim 9 wherein the gas transmitting current collector iscarbon paper.
 11. The proton conducting electrode according to claim 1wherein the catalyst is a porous material impregnated with electronconducting atoms that exhibit electron conductivity.
 12. The protonconducting electrode according to claim 11 wherein the electronconducting atoms include platinum and the porous material is composed ofcarbon powders.
 13. The proton conducting electrode according to claim11 wherein the porous material is impregnated with the electronconducting atoms in an amount ranging from about 1% to about 50% byweight of the porous material.
 14. The proton conducting electrodeaccording to claim 11 wherein the mixture is formed as a layer on a gastransmitting current collector and the electron conducting atoms arepresent on the gas transmitting current collector in an amount rangingfrom about 0.1 mg/cm² to about 10 mg/cm².
 15. The proton conductingelectrode according to claim 1 wherein the fullerene molecules include aspherically-shaped carbon cluster having the general formula C_(m),where m is at least one of 36, 60, 70, 76, 78, 82 and
 84. 16. A methodof producing a proton conducting electrode comprising: coating a mixtureof a fullerene derivative and an electron conducting catalyst on a gastransmitting current collector wherein the fullerene derivative iscomposed of carbon atoms forming fullerene molecules that have a protondissociating group introduced in the carbon atoms; and forming theproton conducting electrode.
 17. The method according to claim 16wherein the proton dissociating group is —XH, where X is an atom havinga divalent bond, and H is a hydrogen atom.
 18. The method according toclaim 16 wherein the proton dissociating group is selected from thegroup consisting of —OH and —YOH, where Y is selected from the groupconsisting of an atom having a divalent bond and a group of atoms havinga divalent bond.
 19. The method according to claim 16 wherein the protondissociating group is selected from the group consisting of —OH, —OSO₃H,—COOH, —SO₃H, —PO(OH)₃ and mixtures thereof.
 20. The method according toclaim 16 wherein the mixture is porous.
 21. The method according toclaim 16 wherein the mixture is coated as a single layer.
 22. The methodaccording to claim 16 wherein the mixture is coated as a multiple layer.23. The method according to claim 16 wherein the catalyst is a porousmaterial impregnated with electron conducting atoms that exhibitelectron conductivity.
 24. The method according to claim 23 wherein theelectron conducting atoms include platinum and the porous material iscomposed of carbon powders.
 25. The method according to claim 23 whereinan amount of the electron conducting atoms in the porous material rangesfrom about 1 wt % to about 50 wt %.
 26. The method according to claim 23wherein the electron conducting atoms are present on the gastransmitting current collector in an amount ranging from about 0.1mg/cm² to about 10 mg/cm².
 27. The method according to claim 16 whereina mixing ratio by weight of the fullerene derivative and the catalyst inthe mixture ranges from about 1:100 to about 100:1.
 28. The methodaccording to claim 16 wherein the mixture has a porosity of about 1% toabout 90%.
 29. The method according to claim 16 wherein the gastransmitting current collector is carbon paper.
 30. The method accordingto claim 16 wherein the fullerene molecules include a spherically-shapedcarbon cluster having the general formula C_(m), where m is at least oneof 36, 60, 70, 76, 78, 82 and
 84. 31. An electro-chemical devicecomprising a first electrode, a second electrode and a proton conductordisposed between the first and second electrodes, wherein at least oneof the first electrode and second electrode includes a proton conductingelectrode including a mixture that includes an electron conductingcatalyst and a fullerene derivative composed of carbon atoms formingfullerene molecules that have a proton dissociating group introducedinto the carbon atoms.
 32. The electrochemical device according to claim31 wherein the proton dissociating group is —XH, where X is an atomhaving a divalent bond, and H is a hydrogen atom.
 33. Theelectrochemical device according to claim 31 wherein the protondissociating group is selected from the group consisting of —OH and—YOH, where Y is selected from the group consisting of an atom having adivalent bond and a group of atoms having a divalent bond.
 34. Theelectrochemical device according to claim 31 wherein said protondissociating group is selected from the group consisting of —OH, —OSO₃H,—COOH, —SO₃H, —PO(OH)₃ and combinations thereof.
 35. The electrochemicaldevice according to claim 31 wherein the mixture is porous.
 36. Theelectrochemical device according to claim 31 wherein the mixture iscoated as a single layer.
 37. The electrochemical device according toclaim 31 wherein the mixture is coated as a multiple layer.
 38. Theelectrochemical device according to claim 31 wherein the mixture isformed as a layer on a gas-transmitting current collector.
 39. Theelectrochemical device according to claim 38 wherein the gastransmitting current collector is carbon paper.
 40. The electro-chemicaldevice according to claim 31 wherein a mixing ratio by weight of thefullerene derivative and the catalyst in the mixture ranges from about1:100 to about 100:1.
 41. The electro-chemical device according to claim31 wherein the mixture has a porosity of about 1% to about 90%.
 42. Theelectrochemical device according to claim 31 wherein the catalyst is aporous material impregnated with electron conducting atoms that exhibitelectron conductivity.
 43. The electro-chemical device according toclaim 42 wherein the electron conducting atoms include platinum and theporous material is composed of carbon powders.
 44. The electro-chemicaldevice according to claim 42 wherein the amount of the electronconducting atoms impregnated in the porous material ranges from about 1wt % to about 50 wt %.
 45. The electro-chemical device according toclaim 42 wherein the mixture is formed as a layer on a gas-transmittingcurrent collector and the electron conducting atoms are present on thegas transmitting current collector in an amount ranging from about 0.1mg/cm² to about 10 mg/cm².
 46. The electro-chemical device according toclaim 31 wherein the fullerene molecules comprise a spherically-shapedcarbon cluster having the general formula C_(m), where m is an integerselected from the group consisting of 36, 60, 70, 76, 78, 82, 84 andcombinations thereof.
 47. The electro-chemical device according to claim31 wherein at least one of said first and second electrodes is a gaselectrode.
 48. The electrochemical device according to claim 31 whereinthe device is constructed as a fuel cell.